1. 1 Challenge the future Master Thesis at SKF: Lateral force estimation acting at a vehicle wheel using a hub bearing unit equipped with strain gauges and Eddy-current sensors By: John den Engelse Date: 19 – 6 - 2013

2. 2 Challenge the future Presentation overview Introduction Research goals Strain gauge measurements Eddy-current sensor measurements Field- / validation measurements BETSY calibration method Conclusions

3. 3 Challenge the future Introduction 1

4. 4 Challenge the future Introduction: Load Sensing Bearing (LSB) Why would we like to measure forces? Monitoring the mechanical loads of a bearing. Control the active safety systems in vehicles like the ABS (longitudinal force) and ESC (lateral force). Measure the vertical load in, for instance, trucks. Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - …

5. 5 Challenge the future Introduction: Load Sensing Bearing (LSB) How?  A load sensing hub bearing unit instrumented with: 6 strain gauges: deformation of the bearing outer ring. 2 Eddy-current sensors: tilting movement of the ABS-ring. Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - …

6. 6 Challenge the future Research goals 2

7. 7 Challenge the future Research goals 1) Lateral force estimation, acting at a vehicle wheel, using strain gauges and Eddy-current sensors. Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - … 2) Calibration of the load sensing bearing using the Bearing Test System (BETSY)

8. 8 Challenge the future Strain gauge measurements 3

9. 9 Challenge the future Strain gauge measurements The strain gauges measure the deformation of the bearing outer ring at six places along the circumference. The deformation provides information about the loads acting on the bearing. Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - …

10. 10 Challenge the future Strain gauge measurements Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - … So what happens?

11. Warning The following slide features a mathematical trick performed by a professional and under the supervision of a professional. Accordingly, the TU Delft and the students must insist that no one attempt to recreate of re-enact any trick or activity performed on this slide.

12. 12 Challenge the future Strain gauge measurements: MLRA Multivariate Linear Regression Analysis (MLRA): The output is assumed to be a linear combination of the input and higher order terms of the input. Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - … For one single dimension: For multi input multi output

13. 13 Challenge the future 1) Absolute value problem 2) Difference in sensitivity for F y 0 N 3) Difference in response for 0 Hz < f < 1 Hz and 1 Hz < f < 10 Hz Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - … Strain gauge measurements: MLRA

14. 14 Challenge the future Strain gauge measurements: F y estimation block diagram Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - …

15. 15 Challenge the future Eddy-current sensor measurements 4

16. 16 Challenge the future Eddy-current sensor measurement Why (inductive) Eddy-current sensor measurements? The strain gauges are subject to the absolute value problem. Strain measurements are subject to low frequent thermal influences. Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - …

17. 17 Challenge the future ABS-ring integrated in the seal of the bearing. 48 holes and 48 spokes. The tilting movement of the ABS-ring gives an estimate of the lateral force F y acting on the bearing. Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - … Eddy-current sensor measurement

18. 18 Challenge the future Two Eddy-current sensors are mounted into the knuckle. Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - … Eddy-current sensor measurement

19. 19 Challenge the future Eddy-current sensor measurement: Signal The change in the lower values provides the information about F y Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - …

20. 20 Challenge the future Eddy-current measurement: Low value algorithm Algorithm to retrieve these lower values. Based signal derivative Maximum change per time sample ∆y max An initial condition y 0 (the equilibrium value) The wheel speed Discontinious output Continuous output Introduction – Research goals – Strain gauge measurements – Eddy-current sensors measurements – Field- / validation measurements - …

21. 21 Challenge the future Field measurements 5

22. 22 Challenge the future Field measurements The LSB equipment has been built in a BMW E60 and tests have been performed at the test track at SKF …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

23. 23 Challenge the future Field measurements Movie: Circle run at 30 km/h …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

24. 24 Challenge the future Field measurements A Kistler VELOS force measuring wheel is used as reference …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

25. 25 Challenge the future Field measurements: Tilt vs F y Eddy-current sensor measurement. …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions N N Data is approximated by a 2nd and a 6th order polynomial: Accuracy vs extrapolation characteristics

26. 26 Challenge the future Field measurements Strain measurement …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

27. 27 Challenge the future Field measurements : F y estimation Two force estimation algorithms. Both for an in-situ calibration and a BETSY calibration. 1) Using 4 MLRA on the strain gauges and use the Eddy- current sensors for the determination of the direction. 2) Using both the Eddy-current sensors and the strain gauges for the force estimation. …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

28. 28 Challenge the future Field measurements : Algorithm 1 …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions Using 4 MLRA on the strain gauges and use the Eddy-current sensors for the determination of the direction.

29. 29 Challenge the future Field measurements: Algorithm 2 Using both the Eddy-current sensors and the strain gauges for the force estimation …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

30. 30 Challenge the future Field measurements : F y estimation, result Estimated force vs time for both algorithms. …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

31. 31 Challenge the future Field measurements : F y estimation, result Estimated force vs measured force for both algorithms. …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

32. 32 Challenge the future Field measurements : F y estimation, result Estimation errors Frequency contentMethodRMS Error [N]Error [%] 0 Hz - 1 Hz MLRA188,8216,46 Tilt 2nd order229,8420,04 Tilt 6th order174,4715,21 In-situ calibration …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions Frequency contentMethodRMS Error [N]Error [%] 1 Hz - 10 HzMLRA130,89141,82 Frequency contentMethodRMS Error [N]Error [%] 0 Hz - 10 HzAlgorithm 1232,0020,09 0 Hz - 10 HzAlgorithm 2216,8218,78

33. 33 Challenge the future BETSY calibration 6

34. 34 Challenge the future Strain gauge measurements: BETSY What is BETSY and why do we want to use it? The Bearing Test System is a 5 Degree of Freedom (DoF) system, where forces and moments are applied in 5 DoF by hydraulic actuators. …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

35. 35 Challenge the future BETSY calibration: strain ε BETSY = c 3 ∙ F y + c 4 ε vehicle = c 1 ∙ F y + c 2

36. 36 Challenge the future BETSY calibration: Eddy-current sensors Good!

37. 37 Challenge the future Field measurements : F y estimation, result Estimated F y vs time for both algorithms …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

38. 38 Challenge the future Field measurements : F y estimation, result Estimated F y vs measured F y for both algorithms. …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

39. 39 Challenge the future Field measurements : F y estimation, result Estimation errors using a BETSY calibration So we can use BETSY for calibration? …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions Frequency contentMethodRMS Error [N]Error [%] 0 Hz - 10 HzAlgorithm 1335,2929,04 0 Hz - 10 HzAlgorithm 2374,5532,44 Frequency contentMethodRMS Error [N]Error [%] 0 Hz - 1 Hz MLRA191,4416,69 Tilt 2nd order261,2322,78 Tilt 6th order342,6429,88 Frequency contentMethodRMS Error [N]Error [%] 1 Hz - 10 HzMLRA265,34287,49

40. 40 Challenge the future Reproducibility: strain Reproducibility is necessary for calibration of a whole production line of LSB …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions Not good! 

41. 41 Challenge the future Reproducibility: Eddy-current sensors Reproducibility is necessary for calibration of a whole production line of LSB …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions Good! 2011 2012

42. 42 Challenge the future Conclusions 7

43. 43 Challenge the future Conclusions: lateral force estimation In the semi-static frequency range the strain gauges as well as the Eddy-current sensors can be used for force estimation with errors ranging from 15 % - 20 %. …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions In the dynamic frequency range the lateral force is not correlated with the strain and ABS-ring deflection. Regarding the Eddy-current sensors BETSY can be used for calibration. Regarding the strain gauges sensors BETSY cannot be used for calibration.

44. 44 Challenge the future Questions? Thank you for your attention !

45. 45 Challenge the future Backup slides

46. 46 Challenge the future Introduction: Load Sensing Bearing What forces act on a vehicle? 3 forces: F x = longitudinal force F y = lateral force F z = vertical force 3 moments: M x = moment around the x-axis M y = moment around the y-axis M z = moment around the z-axis

47. 47 Challenge the future Strain gauge measurements: Applied loads Cycle consisting of 24 load steps. Load steps with 10 seconds of duration. Between each load step a 10 seconds interval of running without load is inserted. Combinations of static and dynamic forces are applied.

48. 48 Challenge the future Strain gauge measurements: Signal conditioning process Filtering Static offset and drift Inverted signal strain gauge 3 No-load intervals Scaling to physical dimensions

49. 49 Challenge the future BETSY calibration BETSY Some differences are present How can we compensate for those differences. Field BETSY and field …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions

50. 50 Challenge the future BETSY calibration By describing both sides of the V-shape by a 1st order polynomial two coefficients, C a and C b, can be derived for both positive and negative F y to transform te one to the other. (So 4 coefficients in total). Ε left,BETSY = c 1,left ∙ F y,left + c 2,left ε right,BETSY = c 1,right ∙ F y,right + c 2,right Ε left,field = c 3,left ∙ F y,left + c 4,left ε right,Field = c 3,right ∙ F y,right + c 4,right BETSY Field

51. 51 Challenge the future BETSY calibration By describing both sides of the V-shape by a 1st order polynomial two coefficients, C a and C b, can be derived for both positive and negative F y to transform te one to the other. (So 4 coefficients in total). ε left = c 1,left ∙ F y,left + c 2,left ε right = c 1,right ∙ F y,right + c 2,right

52. 52 Challenge the future BETSY calibration: Eddy-current sensors

53. 53 Challenge the future Estimation errors distributions

54. 54 Challenge the future Summary: lateral force estimation …– Eddy-current sensors measurements – Field- / validation measurements – BETSY calibration method - Conclusions 0 Hz – 1 Hz CalibrationStrainTilt 2 nd order fitTilt 6 th order fit In-situ16.5 %20.0 %15.2 % BETSY16.7 %*22.8 %29.9 % F y estimation summary:

55. 55 Challenge the future Recommendations Errors obtained with estimation using the Eddy-current sensor are mainly caused by the rubber seal and low value algorithm. This research focused on F y. Next: F x, F z Online testing Excite with higher amount of dynamic forces

56. 56 Challenge the future Questions? Thank you for your attention !

57. 57 Challenge the future Questions? Thank you for your attention !